1. Field of the Invention
The present invention relates to an image forming apparatus and an image forming method using the same and, particularly, to an image forming apparatus excellent in the prevention of white streaks in gray images even if a conductive brush is used as a pre-charging means.
2. Related Art
Conventionally, image forming apparatuses used in such as printers and copy machines used an image forming process, in which a charging means for charging the electrophotographic photoconductor, an exposure means for exposing the charged the surface of the photoconductor to form an latent image, a developing means for transferring toner to the latent image to develop it, a transferring means for transferring the toner to a recording paper to produce an image, and a discharging means for removing residual potential on the surface of the photoconductor after the transfer are arranged around the photoconductor.
In such an image forming process further, the reversal development technique in which a charge opposite to that of the surface of the photoconductor is applied for transferring the toner image to a recording paper is used. The reversal development technique sometimes leads to so-called transfer memory on the surface of the photoconductor after the transfer, which is a residual potential of a charge opposite to that of the surface of the photoconductor.
Although the transfer memory is removed by the subsequent discharging means, a small quantity of transfer memory that is not completely removed by the discharging means accumulates inside the photoconductor after repeated use, causing deterioration in image properties.
On the other hand, when a contact charging system is used as the charging means, the entire constitution is simplified in comparison with a non-contact charging system and no harmful substances such as ozone generate, which has a properties of a tolerance for environments, while a wide charge saturation range is not obtained. Therefore, it is difficult to use a contact charging system to a monolayer type electrophotographic photoconductor excellent in the productivity.
In order to solve the above problems, as shown in FIG. 13, an image forming apparatus 100 using the reversal development system comprising a primary contact charging roller 102, a developing means 104, a transferring means 106, and a pre-exposure lamp 109 has been proposed, in which a contact pre-charging roller 108 that is charged to the same polarity as the charging roller 102 is arranged upstream of the charging roller 102 so that the surface of the photoconductor charged opposite to that of the contact primary charging roller is boosted to the same polarity to remove the transfer memory (for example, see Patent Document 1).
[Patent Document 1] JP-H6-83249A (Claims and FIG. 1)